Electric plugs



July 9, 1968 J. D. GREGORY 3,391,567

ELECTRIC PLUGS Filed May 2, 1966 15 Z /76-2 3:123: /76 2 v 15 a 76 72 v p75 34 $111 $323 My. 3.

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JOHN DENYS GREGORY.

ATTORNEY.

United States Patent "ice 3,391,567 ELECTRIC PLUGS John Denys Gregory, Barrow-in-Furness, England, as-

signor to Oxyley Developments Company Limited, Ulverston, England, a British company Filed May 2, 1966, Ser. No. 546,782 Claims priority, application Great Britain, May 14, 1965, 20,390/65 Claims. (Cl. 72-367) mum.

A method of forming from an elongate metal workpiece, a conductive pin for fitting in an electrically insulating plug body of an electrical plug, comprising in combination the following steps,

machining one end of the metal workpiece to round it off at that end, removing metal from the rounded end to form mutually perpendicular diametral slots of inwardly reducing section, directed along the length or" the workpiece and having their greatest width at said rounded end, forming similarly mutually perpendicular diametral slits in alignment with said slots along a major part of the remaining length of the workpiece, and

applying a conical closing tool to the slotted end of the workpiece to close the segments thereof into abutment against one another and to buckle the segments to form a banana shape,

This invention concerns electric plugs.

Description 0] the prior art It is well recognised that in order to achieve low contact resistance when an electric plug is inserted into a co-operating socket member, a degree of resilient engagement must be provided between the two, and for this purpose the electrically conductive element of the plug, often referred to as the pin, is commonly made of hifurcated construction in a resilient metal. In this way the limbs of the pin are able to yield slightly in order to resiliently engage the wall of a socket when the plug is inserted therein. In a development of this construction, usually employed as a so-called wander plug, the pin is divided along its length, not simply in one plane but in two planes at right angles to one another presenting four mutually yieldable limbs which generally are bulged slightly intermediate ttheir ends. Plugs having single pins of this nature are known as banana plugs.

Summary of the invention The invention seeks to provide an improved method of manufacturing pins primarily although not exclusively for banana plugs, since it will be appreciated that pins of this nature may with advantage be employed in many types of multiple pin plugs.

According to the present invention, a method of forming a conductive pin for an electric plug comprises machining one end of an elongate metal workpiece to round it off at that end, removing metal from the rounded end to form mutually perpendicular diametral slot of inwardly reducing section directed along the length of the workpiece and having their greatest width at said rounded end, forming similarly mutually perpendicular diametral slits in alignment with said slots along a major part of the remaining length of the workpiece and applying a conical closing tool to the slotted end of the workpiece to close the resulting segments thereof into abutment 3,391,567 Patented July 9, 1968 against one another and to buckle the segments to form a banana shape, By virtue of the method provided by the invention, the pin is machined from a single piece of solid material, resulting in a robust and stable component of high dimensional accuracy. Moreover, since the limbs of the pins are not required to be bent to any significant extent, even at their free ends, the initial resilience of the metal is fully retained.

Brief description of the drawings The invention will now be described further by way of example with reference to the accompanying drawings, in which:

FIGS. 1a and l are side and end views, respectively, of a workpiece,

FIGS. 2a and 2 contain two similar views of the Workpiece after flange has been formed,

FIGS. 3:: and 3 contain two similar views of the workpiece aftcr one end has been formed with a screw thread,

FIGS. 4a and 4 contain two similar views of the workpiece after the opposite end has been rounded,

FIGS. 5a and 5 contain two similar views of the workpiece aiter two mutually perpendicular diametral slots have been formed in the rounded end,

FIGS. 6a and 6 contain two similar views of the workpiece after the two slots have been extended to form diametral slits along the major portion of the length of the plug element, together with a cross-sectional schematic view of a closing tool, and

FIGS. 7a and 7 illustrate the work piece after the rounded end has been closed by the closing tool.

Description of the preferred embodiments In a preferred method of carrying the invention into effect, a workpiece 10 comprises a length of metal severed from circular section rod stock of appropriate initial diameter, see FIGS. la and 1. The workpiece is threaded at one end 12, see FIG. 3a to enable it to receive a cap, sleeve or equivalent member of electrically insulating material (not shown) and is formed with a rounded opposite end of truncated, hemispherical shape 14, see FIG. 4a. Prior to the threading and rounding operations, as shown in FIGS. 2:: and 2 the workpiece is machined to present an annular flange 16 adjacent the end which is subsequently to be threaded, the diameter of the workpiece on each side of the flange 16 thereby being reduced. In addition blind bores 15, 17 are formed in the workpiece one from each end, for example by drilling. The rounded end 14 having been formed on the workpiece by a further machinin operation, that end is then formed with a pair of mutually perpendicular diametrical slots 18 of wedgelike shape directed along the length of the workpiece with their apices innermost as illustrated in FIGS. 5a and 5. imilarly perpendicular but parallel-sided slots 20 are then cut along the remaining length of the workpiece approximately as far as the annular flange 16 (see FIG. 6a). This results in the production in the workpiece of [our individual limbs 22 upstanding from the annular flange and terminating in open segmented ends as is clearly shown in the end view of the plug element of FIG. 6. The next and final operation is therefore to close those ends to produce the typical banana shape as at 26 in FIG. 7a, and this is effected by applying a conically socketed closing tool 24 (see FIG. 6a) to cause them to close together under pressure. During this latter operation the partly-formed pin is conveniently held in a jig (not shown) from which the segmentally slotted end projects to an extent determined by the abutment of the annular flange against another part of the jig.

As mentioned above, since the pin is produced from the solid metal, it is strong and durable in service, while the machining operations allow it to be produced to very close tolerance dimensions, contributing to low contact resistance engagement with a co-operating socket. Etfective long term resilient engagement of the limbs with the socket wall is also preserved by the absence of any severe bending operations, which might tend to impair and weaken the metal structure. Typical preferred metals for the manufacture of the pin are brass and phosphor bronze which, while being soft enough to permit the closing of the free end segments of the'pin by a cold forming operation, are hard enough to display a satisfactory resilience. This is particularly important since the application of the conical closing tool to the pin end is intended to exert a force suflicient not only to close the end segments together but also slightly to bulge the limbs to produce a more positive banana shape as illustrated at 26 in FIG. 7a.

I claim:

1. A method of forming from an elongate metal workpiece, a conductive pin for fitting in an electrically insulating plug body of an electric plug, comprising in combination the following steps,

machining one end of the metal workpiece to round it off at that end, removing metal from. the rounded end to form mutually perpendicular diametral slots of inwardly reducing section, directed along the length of the workpiece and having their greatest width at said rounded end,

forming similarly mutually perpendicular diametral slits in alignment with said slots along a major part of the remaining length of the workpiece, and

applying a conical closing tool to the slotted end of the workpiece to close the segments thereof into abutment against one another and to buckle the segments to form a banana shape.

2. A method as set forth in claim 1 further comprising,

forming a screw thread at the end of the workpiece remote from said one end thereof for fitting in a threaded bore in the plug body.

3. A method as set forth in claim 2 further comprising, forming an annular flange between the threaded and slitted portions of the. pin said flange forming a stop to prevent the pin from being screwed too far into the plug body.

4. A method as set forth in claim 3 further comprising, forming a first blind bore coaxially in the workpiece from said one end thereof to extend axially at least as for as said diametral slits.

5. A method as set forth in claim 4 further comprising, forming a second blind bore coaxially to the workpiece from the end remote from said one end thereof towards the annular flange, to provide a recess for solder to form a solder bath for soldering wire to the pin.

References Cited UNITED STATES PATENTS 1,671,540 5/1928 Monteil. 2,004,555 6/1935 Kleinmann et al. 2,036,759 4/1936 Kleinmann.

FOREIGN PATENTS 210,082 9/ 1957 Australia. 607,506 3/ 1926 France. 828,535 2/1938 France. 1,279,360 11/1961 France.

238,655 8/1925 Great Britain. 241,785 10/1925 Great Britain.

MARVIN A. CHAMPION, Primary Examiner.

P. TEITELBAUM, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,391,567 July 9, 1968 John Denys Gregory It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, line 4, "Oxyley Developments Company Limited," should read Oxley Developments Company Limited,

Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

